FPCBs are widely used in various kinds of electronic devices. The FPCB usually comprises a copper wiring layer. A surface of the copper wiring layer is usually treated by chemical plating of nickel and gold to form a nickel chemical-plating layer and a gold chemical-plating layer, thereby increase corrosion resistance of the FPCB.
However, when the copper wiring layer has a minimal line space, the line space may further decrease due to existence of the nickel chemical-plating layer, which may increase the risk of ion migration from the copper wiring layer.